1. Field of the Invention
The present invention relates to a presentation device used in a combination with an overhead projector for projecting an image on a screen and, more particularly, to a presentation device placed on the stage of the overhead projector and used in place of a reference such as an original or a graph.
2. Description of the Related Art
An overhead projector is used to enlarge and project a reference on a screen in a place where many people gather, such as a conference, a lecture, and a seminar. Therefore, the overhead projector includes a projector unit which has a transparent stage for placing a reference, a light source incorporated in the projector unit to emit light through the stage. The overhead projection further includes a magnifying reflecting mirror disposed outside the projector unit and above the stage to reflect the light passing through the stage, i.e., the reference, onto the screen.
In the above-mentioned overhead projector, a reference to be placed on the stage must be a transparent film in which data to be projected is written, in consideration of the principle of projection to the screen. For this reason, when the overhead projector is used, it takes long time to prepare the reference. In addition, when the number of pages of the reference to be projected is large, it also takes long time to change the reference on the stage.
In consideration of the above situation, recently, a panel unit including a transmissive-type liquid crystal panel is available in place of a reference of a transparent film. More specifically, a panel unit, i.e., a liquid crystal panel is connected to a so-called personal computer, in particular, to a portable personal computer, and is usable as a presentation device of the personal computer. Therefore, the liquid crystal panel of the panel unit receives an image signal from the personal computer, and can present an image in response to the image signal.
When the above-mentioned panel unit is used, it is placed on the stage of the overhead projector. However, the liquid crystal panel of the panel unit tends to be adversely affected by heat from the light source in the overhead projector. For this reason, a cooling fan as in the above personal computer may be disposed in the panel unit. If such a cooling fan is disposed, outer air can be forcibly introduced in the panel unit. The introduced air is exhausted from the panel unit, so that the liquid crystal panel in the panel unit can be cooled with air.
As described above, the liquid crystal panel in the panel unit is forcibly cooled with air, so that the adverse effect on the liquid crystal panel due to heat is considerably reduced. However, in this case, dust in the air fed in the panel unit is attached to the upper and lower surfaces of the liquid crystal panel and the inner surfaces of a pair of transparent protective covers which are disposed on the panel unit. For this reason, when the panel unit is used, the upper and lower surfaces of the liquid crystal panel and the inner surfaces of the pair of transparent covers must be constantly cleaned.
The above-mentioned pair of transparent protective covers, however, are integrally formed with a casing of the panel unit, or are mounted to the casing with set screws, in the normal case. Therefore, the abovementioned cleaning cannot be easily performed.